Process for making transducer devices having bonded elements



May 19, 1953 A. SZEGVARI ET AL PROCESS FOR MAKING TRANSDUCER DEVICESHAVING BONDED ELEMENTS Filed May 5, 1950 IN VEN TOR.

ANDREW SZEGVARI BY CHARLES K.GRAVLEY ATTORNEY not highly elevated, andwhich is in a state of molecular dispersion in a quantity of apolymerizable liquid solvent material to increase the liquidity of thebonding material and permit a satisfactory bonding contact withelemental areas of the aforesaid surfaces in spite of the substantiallylarge average molecular size of the par tially polymerized bondingmaterial. The process further comprises placing the two surfaces oneagainst the other with the introduction therebetween of a catalyst toeffect a polymerization reaction involving simultaneously the partiallypolymerized bonding material and the polymerizable solvent material at atemperature under 90 0. without evolution of any volatile material,thereby effecting strong adhesion of the two surfaces.

For a better understanding of the present invention, together with otherand further objects thereof, reference is had to the followingdescription taken in connection with the accompanying drawing, and itsscope will be pointed out in the appended claims.

In the drawing,

Fig. 1 is a perspective view partially cut away, of an expandertransducer device assembled in accordance with the process of theinvention; and

Fig. 2 is a perspective view of a series-connected bender transducermade in accordance with the invention.

Referring to Fig. 1 of the drawing, there is shown a transducer assemblyincluding a base surface II on which rests a block or bar it ofpiezoelectric material. The bar [2 rests on the base H at a surfaceportion I3 of the base H, visible where a corner portion of the bar Ithas been cutaway. The bar I2 is provided with electrodes l4 and [5 onindividual opposed surfaces of the bar. The bar [2 may be cut from asingle crystal of Rochelle salt in a well known manner so thatdistortion of the bar, involving a vertical movement of the uppersurface of the bar, as indicated by the double arrow, is associated withthe application or appearance of an electrical voltage or charge at theelectrodes I l and IS. The length dimension of the bar is assumed to bethe vertical dimension in Fig. l, but it is understood that thisvertical dimension of the bar may be considerably smaller and may evenbe the thickness dimension of the bar. The bar l2 resting on the surfaceI I may be placed in a body of liquid such as oil, in which casemovements of the upper surface of the bar are communicated to the liquidand may cause the generation of,

acoustical elastic wave energy in the liquid. Many forms of suchelectroacoustical transducers are known to the art. For example, anumber of other bars, not shown, similar to the bar 12 may be placed onthe base surface I l side by side with the bar I2 and their respectiveelectrodes connected to the same source of electrical energy. The topsurfaces of such a plurality of piezoelectric bars may be connnected toa relatively large diaphragm, not shown, covering all of the bars toobtain the desired acoustical coupling to a fluid or liquid medium.

In such devices it is necessary that the lower surface of the bar l2 andof any similarly arranged bars in the electroacoustical transducer bewell secured to the base H at the surface or surfaces l3 of contact, Notonly must the assembly remain secure during transportation and in use,even if the base surface H is turned on its side or is turned over so asto face vertically downward, but also the bond must be secure againstacoustical vibrations in the liquid, to which the free end surface ofthe bar is coupled and which may exert forces on the bar tending to pullit away from the base ll. The process of the invention for making atransducer device such, for example, as the device in which theelectromechanically sensitive element 12 is secured to the surface itwill be described in detail hereinbelow.

Referring now to Fig. 2 of the drawing, there is shown aseries-connected bending-sensitive transducer assembly of the sandwichtype including a base 2 l. The transducer also includes twoelectromechanically sensitive elements 22 and 23. A major surface of oneof these elements is placed against a major surface of the otherelement, and one end portion of the resulting assembly is fastenedwithin a depression machined in the base 2|. This fastening may beaccomplished by clamping, by the insertion of shims around the endportion of the electromechanically sensitive assembly, or with the useof the cementing procedure specified in accordance with the presentinvention as described in detail hereinbelow. The exposed or outer majorsurfaces of the elements 22 and 23 are provided with respectiveelectrodes Z l and 26, a portion of the latter being visible in Fig. 2where the electrode 24 and the elements 22 and 23 have been cut away.The free end portion of the composite element assembly is provided witha channel member 21 clamped se curely thereover. To the channel memberis fastened, as by welding, a rod 28.

The electrodes 25 and 25 may be connected to respective electricalterminals, not shown, Any voltage appearing across such electrodes is applied in series across the elements 22 and 23. For this reason thecomposite sandwich element may be called a series-connected sandwichtype trancducer. The elements 22 and 23 may be plates cut from singlecrystals of a piezoelectric sub stance such as Rochelle salt or ammoniumdihy drogen phosphate. The two plates may be identi cal, but duringassembly the plates are turned so that the thickness directions of thetwo plates are oriented oppositely with respect to the piezo electricaxes of the crystalline substance. Accordingly one plate tends to expandwhile the other contracts, so that an electric field across the platesis associated with piezoelectric deformations of the regions near thetwo adjacent surfaces in opposite senses, these deformations in turnbeing associated with flexural movements of the composite element,specifically bending movements of vertical lines in the compositeelement as seen in Fig. 2. When the composite element bends, the rod 28moves axially, as indicated by the double arrow. Likewise forces appliedare ially to the rod 28 are transmitted through the channel 2'5 to causeover-all bending movements of the composite element, one element beingelongated While the other element is shortened. This is the same type oftransducer device illustrated in Figs. 4 and 5 of the Sawyer reissuepatent, referred to hereinabove.

In sandwich type transducer devices such as that shown in Fig. 2, itfrequently is desirable to electrode the inner surfaces of each of theplates 22 and 23 before placing them together. This permits a parallelrather than a series connection of the two elements. Moreover, very thinelectrodes of finely divided conductive particles may be applied to makeintimate contact with the surfaces, so that when the two electrodedsuracacgzv:

faces-are placed incontact each other there are no spaces between the#crystalline surfaces? across which? voltage. drops mightidevclop. due'to the relatively low' dielectric rconstants of f che-1 cc- In suchcases it is customarymenting materials. to leave substantialunel'ectrodedamargins:around theedges of: thezopposedsurfaces; When1these partially" electroded surfaces I are-placed in: prose imity toeach other; a'nnarticularlya strong. bond: may be achievedinaccordancewith'theipresentf invention between the unelectroded marginalsurface portions of. the. two-single-crystalline plates of piezoelectricmaterial. The bonding process" described" hereinbelow: also producesvery good bond between electrodedcportions 'a of the two crystal.surfaces.

The :DIOCCSS in' accordance with the invention== for making.atransducerdevice, suchv as-thedevice-in: which the electromechanicallysensitive elementsli and 23 ofFig. 2.are'securedtozeach other,. nowwill. be described.

polymerized to enable furtherirapidpolymerization for bonding purposesat temperatures not highly elevated. If a monomeric compound such as themonoester of a dicarboxylic acid and a glycol were used as the bondingmaterial, or if a slightly polymerized material such as the dimer ofsuch a monoester were used,.thetpolymerizae Y ,7

tionineeded to. aehieveacsatisiactory bond "is .so

extensive that inconveniently r large periods of 5 time, or temperaturesso elevated as to 'be'damaging 5 to piezoelectric crystals; or 'both;would be required to make the bonding; material A set or;

harden.- However, the partially polymerized'maaterials"whichiconvenientlyamay: be further :poly; merized have1ost'1t0.'a" noticeable extent. their? ability'sastliquids .to .spreadsover the surfaces-ate. bevb'onded tand to penetrate toiall minute-poretionsof such. surfaces. Accordinglythe partial.- I 1y polymerized rbonding. material .is applied to at "least one'of ithesesuriaces in'a:state of moles-:- ular dispersion m :a quantity of a rpolymerizablesrliquidxsolvent material to increase the liquidity-oi the "bondingmaterial: and permit. a satisfactory bonding contact"withielementalareas of the sur-v faces :izispite 'of ithe substantially large 1average molecular size. of the partiallygpolymerizedbond-r process.broadly: expressed, then compriseszplacingthe'two surfaces :so treated.one :against the other with the introduction:v therebetweenof a catalystto-efiect a polymeriza tion reactioninvolvingmost or all citric-material1 ing material;

whichhad been. applied, thus eflfe'ctingthe bond,ias describedand-exemplified in detail ihereinbelow.

It would be permissible to include -.between.:the

surfaces to be-secured together some *inertsubstance,v provided thesettingnprocessrcan. beccar riedout ata temperature underQCl C; withoutHowever; its

evolution of any volatile material. I isspreferred. to use only activeor polymerizable substances in the bonding materialfso that. when thesurfaces areplaced together in the presence of the catalyst a.polymerization reaction -is..ef-- fected. involving directly allmaterials used .1 in.

the-bonding operation;

and a'aglycol: The partially polymerized-state 10f the "polyesterbonding material: zpreferably pro; videsmolecular weights :of1the orderof 2000; but.

in any" case the apolyesters should "have "a molec ular weightless1thanabout5000r The condensetion polymerization of the esters ofdicarboxylic acids and dihydric:aloholstd form linear polyesters is wellknown. This polymerization reaction-carrbe made to proceed-smoothly inthe presence of catalysts conventionally used'for this purpose;particularly when the acid and alcohol are present in' fairly pureforms'and in stoichiometrically equivalent amounts.'- An identicalpolyester may ee obtainedwhen' the corresponding imonomeric ester" ormonoester, which is both" anacid ester and "an ester alcohol is formedby" reacting' the glycol with the anhydride'" of the Accordingly" thepreferred process ofthe-present invention'maybej.-carried out usingpolyesters obtained-"from" such anh'yd-r'ides or many other suitablemanner, even particular" dicarboxylic acid.

though the original 'reaction forming the mono ester cannotbe'designated strictly as a condensa The ex pression, apolyester of adicarboxylic-acid and a glycol,"as-used in this'specification andir'rth'e appended claims; is intended to include poly estersihaving thespecified composition whether or not"actually formed'by theesterificationmf" .a di'carb'oxylic acid and'aglycol under polymeriztion or even' an esterification reaction;-

ing conditions: i

The monoester ofa givendicarboxylic acid and a given glycol can beformed. For example,".

equirn'olecular amounts of maleicacid COOILCHE'CHLCOOHY and-.idiethyleneglycol; CHOHCHaOCHz' .CHZOH'; woul'dforma monesterydiethylene glycolmaleate; havingraa' molecular weight or 204,1 having a: hydroxygroupxzatone end ioi the FmoIecuIeand a 'carboxy' group at the other: tend,'iandhaving one olefinic ilinkage r in the molecular chain containing" eight.carbon atoms 1 and the 6 oxygen atom. from: I the diethylene glycol!proximate multiples of the molecular weight of the monoester.

polymerized lpolyester having a. moderate molec-"- ular 7 weight; as vmentioned hereinabove polyester. thus formed may .be :very' viscous; anditsclassificationreitlier as avliquid oras a :solid may not be obvious.from zpolybasicfacids or. anhydri'des anda-polye hydric alcohols-by thecondensation polymeriza tionxofa monoester are'known asalkyd resins."

Viscous,:-parti.ally polymerized resins of this type maybe used"directly as bonding agents by :causing i further polymerizatiom. but,asmentioned" above, :the local mobility and the liquidity'of thematerialare-.sorlow 'that a-goodbond is dificultto achieva;

Therefore, .beforethe. partially polymerized.

bonding .material is used. inwmaking the trans-. ducerdevice in.accordance with. the invention, it isplaced ina-state of moleculardispersion a quantity ofxawpolymerizable. liquid solvent. ma-. 'terial;preferably ,a polymerizable liquid aromatic However," with or withoutsome .fcatalytic action .or rthe raid of tan-'- acceleraton'.thezpolymerization of this mon'oe' esteri'usually proceeds-to some "degree;and so "is carried outat least to 'azsignificant extent. before thematerial is used in the process .of'the present invention; Thuspolyesters areiform'erl having-1 molecular weights which. i presumablyare ape- Accordingly; it is desirable f to carry outfa:=substantial.partial polymerizationrof; the'iesteriflcationi productto ohta in awpartially The Such polyesters formed compound with anolefinic side chain. The individual molecules of the partiallypolymerized material are dispersed in the liquid without chemicalbreakdown of the molecules. A quantity of essentially monomeric styreneCsHs.CI-IICH2 is admirably suited for this purpose, but other compoundsof this type, such as diallyl phthalate, O-CaI-I4(CO.O.CHz.CI-IICH2)2,also are suitable.

When the polyester bonding material is in solution in a quantity ofstyrene, as just described, the resulting material not only has highlocal mobility and in general rather low viscosity but also can bepolymerized quite readily and completely at temperatures not at allhighly elevated. This high liquidity permits easy spreading of thematerial to all portions of the surfaces to be bonded, and it has beenobserved that these polyesters dissolved in styrene tend to wet thesurfaces of the usual electromechanically sensitive elements. Oncehaving spread over and covered these surfaces, the local mobility of thematerial tends to insure active contact of the solution with eachsubmicroscopic portion of the surface of the element. The effectivenessof this active contact seems to be particularly great when the surfacecovered is that of a body of a substance which is polar, so thatespecially good bonding may be obtained when at least one of the twosurfaces to be secured together is cut from a single crystal of a polarcompound.

The phrase a dicarboxylic acid is used herein in the collective sense,and such an acid may contain in admixture or in solution more than onedicarboxylic acid. Likewise, more than one glycol might be used. In suchcases presumably the dicarboxylic acids and the glycols enter the linearpolymeric chain in the approximate relative proportions of theiroriginal molecular ratios. However, it is generally important that,considering all dicarboxylic acid substances present on the one hand andall glycol substances present on the other hand, these substances bepresent originally in stoichiometrically equivalent ratios.

Thus, when the polyester is of the type formed by the condensation of asingle dibasic acid and a single glycol, the polyester may be producedfrom equimolecular, amounts of the particular acid and the particularglycol.

The polyester used advantageously is at least partially olefinic. ofthe: monoester units making up the polyester molecule advantageouslyshould be olefinic. This can be accomplished by using either adicarboxylic acid, Or a glycol, or both, which contains an olefinic acidor glycol, as the case may be.

In a preferred form of the process of the invention, the dicarboxylicacid contains at least substantial portions of an olefinic dicarboxylicacid to provide in the polyester at least a substantial number ofolefinic monoester components, making the corresponding polyester atleast partially olefinic. Accordingly the dicarboxylic acid may containat least substantial portions of maleic acid. The dicarboxylic acid mayconsist solely of an olefinic dicarboxylic acid to make the polyesterproduced by reaction with a glycol under polymerizing conditions anolefinic polyester. When the dicarboxylic acid, contains substantialportions of an olefinic dicarboxylic acid, it may also contain asaturated dicarboxylic acid, such as sebacic acid, COOH(CH2) BCOOH. Thusthe dicarboxylic acid constituents of the In other words, at least somepolyester may contain or consist of sebacic acid and substantialportions of maleic acid, or the olefinic polyester may be the polyesterof a single dicarboxylic acid, preferably maleic acid, and a glycol.

A variety of glyc-ols is available for the formation of the polyesterused in connection with the invention. The simpler glycols arepreferred, and excellent results have been obtained with the olefinicpolyester of ethylene glycol,

CH2OH.CI-I2OH and a dicarboxylic acid containing substantial portions ofmaleic acid. Diethylene glycol may be used, and one o-lefinic polyesterwhich has given particularly good results is the polyester of maleicacid and diethylene glycol, the monoester of which is mentionedhereinabove. It will be understood that the particular polyester justreferred to does not contain in its molecules any appreciable acidic oralcoholic components other than those which may be derived by thepolyesterification mechanism from the specified di' basic acid andglycol; however, it will be clear that identical polyesters, describedand defined by the same names, may be formed with anhydrides instead ofacids, for example, by the use of maleic anhydride,

C0.0H:CH.COO

instead of maleic acid.

After the olefinic polyester has been dissolved in the styrene, it isapplied to at least one of the two surfaces to be secured together.

In a preferred embodiment of the invention, parts by weight of theproduct formed by the condensation of maleic acid and diethylene glycolare dissolved in 30 parts of nominally monomeric styrene by stirringvigorously until a homogeneous solution is obtained. In this form thesolution has a shelf life of several months. The solution is applied toone of the two surfaces,

while a catalyst is applied to the other of the surfaces, so that whenthe two surfaces subsequently are placed one against the other thecatalyst automatically is introduced therebetween and immediately startsto bring about the desired polymerization reaction involvingsimultaneously the partially polymerized polyester bonding material andthe polymerizable solvent styrene material, thereby effecting strongadhesion of the two surfaces. Four parts of a peroxide catalyst in theform of benzoyl peroxide, (C6H5.CO)2O2, may be used with themaleatestyrene solution specified above. This peroxide materialconveniently is dissolved in a non-aqueous solvent and applied in liquidform, for example as a 5% solution in benzene. The liquid catalystsolution is allowed to dry before the surface to which it has beenapplied is pressed against the surface to which the polyester-styrenesolution has been applied.

Other catalysts, mostly of the peroxide type, suitable for use in thepresent process are well known in the art. For example, lauroylperoxide, (CH3(CH2)10CO)2O2, or a cyclic organic peroxide may be used,preferably in combinations with an accelerator such as a cobalt salt ofnaphthenic acids. The polymerization reaction proceeds in a period oftime of the order of one hour, and frequently less than half an hour, toprovide a aeasgacr well set-:bond: of the; plastic: material; and; thissetting 'OCCllISl in l'thec-shortiperiod of time-; ate a temperatureunder--90? C. Usin'gamansi of the specific materials mentioned;hereinabover the polymerization; proceeds inthe neighborhood; of roomltemperature to substantial :zcompletionjnoa short period. of v time, sothat "the: process :of .:the invention is particularly, useful whenmaterials are involved which shouldno-t beysubjected; tohigher-temperatures.

In .another preferred embodimentrot .the'invem tion, .100 partsloyaweightroi 1a partiallyzpolymer: ized polyester materialare.dissolved.in-35 parts of styrene, and about 0.1 part of cobaltnaphthe: natecis added totheliquid. This liquidahasra long shelf rlife.Within :about ;half: an'shour .be.-' fore the time of applying: thesbondingcmaterial, 018 spartx of lauroyl peroxide powdcryis added'atothe-liquidate .a catalyst The resultingzsolutionais appliedpromptly to.both;surfacesdzozhe: secured together, so: that. the catalyst:is;intrduced::be:-. tween the surfaces at 1 the r time 0i applicationalongzwith the bonding: material itself: a The ratazs lyzed 5 materialhasla setting. time of zaboutsthree h0li1S atl50'C., during. which timethe .two sur faces are maintained pressedtogether; This;pro-. cedure,vusing the. specified: materials; has .v been particularly successiul.The polyester. material used lconvem'entlylis: made". up. of: 25. partsof Paraplex A1 48 and 75 parts of: Paraplea A245, these being productsobtainable-efromthe Rohm. ,Sz': Haas Company, Philadelphia. Theseproducts-;are;polyestersrwhichlare essentiallygthe condensationproducts; of. sebacic, acid;v maleic acid, and ethylene. glycol, the"A1948? material having proportionately less of the-.olefinicmaleicacidthan' the -.AP45, material.

While anwunderstanding of thermechan-ism =of thepolymerization reactionis not a part of. the present invention, it Y will appear: that all: thecementing materials ,used; with t the. possible ex-. ception of thecatalyst itself are polymerizable and-:should take an'active partpinthecementing process. This occurswithout evolution of any volatile,material, since no .such material need he presentbetween-the: twosurfacesuwhen they are placed" together." It isV-tbelieved: that,th'e-lstyrene serveslto provide a-substantiahnumber of cross linkages;with linearpolyester: chains; by virtue of the double bonds intheunsaturated polyester and in the styrene itself. Thus the-catalystacts tcpefiect apolymerizationand: cross-linking are: action: Atensileestrengthtgreaterrthan.;that;,0f the piezoelectric a crystalst-themselvessmay; be i chitained, and i the bonding material is quite:res sista-nt .to moisture and non-.aqueous-solvents: In the :usualtransduceri'configurations: the:exot-herev mic natureofthepolymerization reaction "causes onlyr-a small temperaturerise.vThispolymerizae tion' tends-to .b'ecinhibited by air; making-sit .posesible'to-wipeoff 'surpluscement after the joint has set While there havebeen described; whatat present: are. consideredto be the preferred em:bodiments of this'invention; itwillb'e obviousto those skilled intheartthat various-changesand modifications may he: made therein without departing from the invention It is-aimedg: there-1;- fore, inithe appendedclaims to cover all such changes and modifications whichsiall' withinthe true spirit and scope of the inventiom.

What isclaimed is:

1'. The process for'makingatransducerdevice having anelectromechanically sensitive 'element one surfa'ceaof which-is-securedto another similarlyyshaped: surface comprising; applying-to. at least:oneaof :saidrtwo-suriaces. a=bondingmaterial, which ,is.-partial1y;polymerizedt to enable:,:further rapid polymerization, forbonding; purposes.- at temperatures:notihighlyqelevated; and" which: isin a. state. of molecular dispersion :in a l quantity oiaapolymerizaioleilliquid-solvent1materalto: ine crease the liquidityvofzsaidcbonding materialand permitzai.satisfactory; bonding;contactwith ele-J. mental area-snot saidsuriaces in spite lofzthe sub,-stantial-ly large average molecular: size. of a said partiallypolymerized bonding: material; and placing; said two: surfaces vone:against ithe -other with r the introduction; therebetween of; a cata:lyst to effect a polymerization. reaction involving simultaneouslysaidmartially: polymerizedfbondill-g material andsaid polymerizablesolvent mae terial at as temperatureaunder (3.; Wil'ihOll'blEBNOiilutiorr; 0L:any'xvolatilermaterial; thereby i-efiecting strong; adhesionotisaid: twoosuriacesl I 2.; The process for makingatransducer; devicehaving:.an-electromechanically sensitive element one -surfacesof :which;is secured .110. another simie larlyi shapedesurfaceccomprisingapplying .;t0; a,t leastone opsaidtwo surf acesgaapclyester', whichrispartially polymerized; to; enab1e:.:furthe1tr rapid polymerization: forbondingnnurposes .atrtemperaa tures notuhighly elevated, andwhichr-isssin a: state of molecularxdispersionsin a-lquantity oftat-poly merizaelecliquidisolvent material ton-increaselthe liquidity:of: saidrpolyester;'andripermit z ai-satisface toryi bonding contactwith; elemental:v areasr of said surfaces in spite:oiithezsubstantially;large average: molecular: sizes of' said;v partiallypolymerized'ipotyester; tandaplacing:saidztwosurfaces one against; the:other; with; the introduction therebetween. of; aecatalyst 1 to effect apolymer.- ization: reactionr involving simultaneously said partiallyrpolymerized: polyester and} saidLpply merizable;solventunaterial atastemperaturevune der; 90?" C; without evolution of anyzvolatile materiaLr. thereby: eflecting; strong adhesion ;ofsaid two-surfaces:

3s Thezprocessdorvmakingsra.ltransducehdevicehavinggamelectromechanicallyl sensitive element one. surfacerof whichis: securedrtowanother,isimiq larlyo shapedsurfacercomprising; applyingto at least ones of;.; said; two: surfaces an, essentially linearpolyester; whiclhisupartiallyr polymerized torenable' c-fnrt-herlrapidapolymerization' for bonding purposes 1 at; temperatures nothighly. detvated, .andlwhich: issin ;astate:.o-f;molecular; dis:persion:v in; a:.; quantity of a; polymerizable liquid solventxmaterialtomincreasenthe liquidity oflsaid polyesterzand permitga'lsatisfa'ntory,v bonding cona tact: with elemental areas:oflsaidiisurfacesrin spite :of ;.the' substantially large;averagezl-molecu-ve lan: size: 0t: said ipartiallyr polyrnerized:polyester; and aplacingc; said: two; surfaces 1 one against; the others:the introduction; therebetwecn 1,051; a catalyst: to efiects; apolymerization. reactioninvolving; sin'iultaneouslyc said: partially,polymer:- ized: polyester and; said;- polymerizable. solvent material ata temperature under 90 0. without evolutions. of; any; volatilematerial, thereby effecting lstrongzr-adhesion'lof "SQjdTiFWOl surfaces;

4Theaprocess forrmaking-taz .transducerzdevice having an;electromechanical-1y sensitive element one: surfaceco-f ;whicb:-is:securedto ,anothen simie larlyishaped surf ace:- comprising:applyingotcxiat least one: of i said: surfaces :an essentially: linearolefinic polyester; .whi'ch islpartiallyi'polymerized to enablefurtherrapid polymerization for b'onding purposes at temperatures nothighly elevated; ancliwhiclr issin a state of molecular dispersion in aquantity of a polymerizable liquid aromatic compound with an olefinicside chain to increase the liquidity of said polyester and permit asatisfactory bonding contact with elemental areas of said surfaces inspite of the substantially large average molecular size of saidpartially polymerized polyester; and placing said two surfaces oneagainst the other with the introduction therebetween of a catalyst toeffect a polymerization and cross-linking reaction involvingsimultaneously said partially polymerized polyester and saidpolymerizable aromatic compound at a temperature under 90 C. withoutevolution of any volatile material, thereby effecting strong adhesion ofsaid two surfaces.

5. The process for making a transducer device having anelectromechanically sensitive element one surface of which is secured toan other similarly shaped surface comprising: ap-

plying to at least one of said two surfaces a polyester of adicarboxylic acid and a glycol, at least some of whose monoester unitsare olefinic, which has a molecular weight less than about 5000, andwhich is in solution in a quantity of a polymerizable liquid aromaticcompound with an olefinic side chain; and placing said two surfaces oneagainst the other with the introduction therebetween of a catalyst toeffect a polymerization and cross-linking reaction involving saidpolyester and said aromatic compound at a temperature under 90 C.without evolution of any volatile material, thereby effecting strongadhesion of said two surfaces.

6. The process for making a transducer device having anelectromechanically sensitive element one surface of which is secured toanother similarly shaped surface comprising: applying to at least one ofsaid two surfaces a polyester of a dicarboxylic acid and a glycol, atleast some of whose monoester units are olefinic, which a has amolecular weight less than about 5000, and which is in solution in aquantity of styrene; and placing said two surfaces one against the otherwith the introduction therebetween of a peroxide catalyst to effect apolymerization reaction involving said polyester and said styrene at atemperature under 90 C. without evolution of any volatile material,thereby effecting strong adhesion of said two surfaces.

7. The process for making a transducer device having anelectromechanically sensitive element one surface of which is secured toanother similarly shaped surface comprising: applying to at least one ofsaid two surfaces an olefinic alkyd resin which has a molecular weightless than about 5000 and which is in solution in a quantity of styrene;and placing said two surfaces one against the other with introductiontherebetween of a peroxide catalyst to effect a polymerization reactioninvolving said resin and said styrene at a temperature under 90 C.without evolution of any volatile material, thereby effecting strongadhesion of said two sur-. faces.

8. The process for making a transducer device having anelectromechanically sensitive element one surface of which is secured toanother similarly shaped surface comprising: applying to at least one ofsaid two surfaces a polyester of a dicarboxylic acid and a glycol, saiddicarboxylic acid containing at least substantial portions of anolefinic dicarboxylic acid to provide in said polyester at least asubstantial number of olefinic monoester components, making saidpolyester at least partially olefinic, and said polyester havmg amolecular weight less than about 5000 and being in solution in aquantity of styrene; and placing said two surfaces one against the otherwith the introduction therebetween of a peroxide catalyst to effect apolymerization reaction involving said polyester and said styrene at atemperature under C. without evolution of any volatile material, therebyeffecting strong adhesion of said two surfaces.

9. The process for making a transducer device having anelectromechanically sensitive element one surface of which is secured toanother similarly shaped surface comprising: applying to at least one ofsaid two surfaces a polyester of a dicarboxylic acid and a glycol, saiddicarboxylic acid containing a saturated dicarboxylic acid andsubstantial portions of an olefinic dicarboxylic acid to provide in saidpolyester a substantial number of olefinic monoester components, makingsaid polyester partially olefinic, and said polyester having a molecularweight less than about 5000 and being in solution in a quantity ofstyrene; and placing said two surfaces one against the other with theintroduction therebetween of a peroxide catalyst to effect apolymerization reaction involving said polyester and said styrene at atemperature under 90 C. without evolution of any volatile material,thereby effecting strong adhesion of said two surfaces.

10. The process for making a transducer device having anelectromechanically sensitive element one surface of which is secured toanother similarly shaped surface comprising: applying to at least one ofsaid two surfaces a polyester of a dicarboxylic acid and a glycol, saiddicarboxylic acid containing sebacic acid and substantial portions of anolefinic dicarboxylic acid to provide in said polyester a substantialnumber of olefinic monoester components, making said polyester partiallyolefinic, and said polyester having a molecular weight less than about5000 and being in solution in a quantity of styrene; and placing saidtwo surfaces one against the other with the introduction therebetween ofa peroxide catalyst to effect a polymerization reaction involving saidpolyester and said styrene at a temperature under 90 C. withoutevolution of any volatile material, thereby effecting strong adhesion ofsaid two surfaces.

11. The process for making a transducer device having anelectromechanically sensitive element one surface of which is secured toanother similarly shaped surface comprising: applying to at least one ofsaid two surfaces a polyester of a dicarboxylic acid and a glycol, saiddicarboxylic acid containing at least substantial portions of maleicacid to provide in said polyester at least a substantial number ofolefinic monoester components, making said polyester at least partiallyolefinic, and said polyester having a molecular weight of less thanabout 5000 and being in solution in a quantity of styrene; and placingsaid two surfaces one against the other with the introductiontherebetween of a peroxide catalyst to effect a polymerization reactioninvolving said polyester and said styrene at atemperature under 90 C.without evolutionof any volatile material, thereby effectin strong adhesion of said two surfaces.

12. The process for making a transducer device having anelectromechanically sensitive element one surface of which is secured toanother similarly shaped surface comprising: applying .to at least oneofsaid twosurfaces a polyester of a.

- idlcarboxylic acid and a glycol, saiddiciarboxy'lic acid consisting ofsebacic acid and substantial tion in a quantib of styrene; andplacingsaid .two" surfaces one against 'the other with the introductiontherebetween f atperoxide. catalyst to effect a polymerization reactioninvolving said polyester and said styrene at a temperature under 90 C.without evolution of any volatile material, thereby effecting strongadhesion of said two surfaces.

13. The process for making a transducer device having anelectromechanically sensitive element one surface of which is secured toanother similarly shaped surface comprising: applying to at least one ofsaid two surfaces an olefinic polyester of ethylene glycol and adicarboxylic acid containing substantial portions of maleic acid, saidpolyester having a molecular weight less than about 5000 and being insolution in a quantity of styrene; and placing said two surfaces oneagainst the other with the introduction therebetween of a peroxidecatalyst to effect a polymerization reaction involving said polyesterand said styrene at a temperature under 90 C. without evolution of anyvolatile material, thereby effecting strong adhesion of said twosurfaces.

14. The process for making a transducer device having anelectromechanically sensitive element one surface of which is secured toanother similarly shaped surface comprising: applying to at least one ofsaid two surfaces an olefinic polyester of diethylene glycol and adicarboxylic acid containing substantial portions of maleic acid, saidpolyester having a molecular weight less than about 5000 and being insolution in a quantity of styrene; and placing said two surfaces oneagainst the other with the introduction therebetween of a peroxidecatalyst to effect a polymerization reaction involving said polyesterand said styrene at a temperature under 90 C. without evolution of anyvolatile material, thereby efiecting strong adhesion of said twosurfaces.

15. The process for making a transducer device having anelectromechanically sensitive element one surface of which is secured toanother similarly shaped surface comprising: applying to one of said twosurfaces a polyester of a dicarboxylic acid and a glycol, at least someof whose monoester units are olefinic, which has a molecular weightlessthan about 5000, and which is in solution in a quantity of apolymerizable liquid aromatic compound with an olefinic side chain;applying to the other of said surfaces a peroxide catalyst; andsubsequently placing said two surfaces one against the other to effect apolymerization and cross-linking reaction involving said polyester andsaid aromatic compound at a temperature under 90 C. without evolution ofany volatile material, thereby effecting strong adhesion of said twosurfaces.

16. The process for making a transducer device having anelectromechanically sensitive element one surface of which is secured toanother similarly shaped surface comprising: applying to at least one ofsaid two surfaces an essentially linear olefinic polyester, which ispartially polymerized to enable further rapid polymerization for bondingpurposes at unelevated temperatures, and

i114 which. is ina state. of molecular: dispersiona quantity of apolymerizable liquid aromatic compound with an olefinic side chain toincrease the liquidity of said polyester and permit a satisfactorybonding-contact with elemental areas of said 'surfaces'in spite of thesubstantially large average molecular size of said partially polymerizedpolyester; and placing said two surfaces one against the other with theintroduction therebetween of a catalyst to effect a'polymerizationandcross-linking. reaction involving simultaneously. saidpartiallypolymerized polyester and said polymerizable aromatic compound at atemperature in the neighborhood of room temperature without evolution ofany volatile material, thereby effecting strong adhesion of said twosurfaces.

17. The process for making a transducer device having anelectromechanically sensitive element one surface of which is secured toanother similarly shaped surface comprising: applying to at least one ofsaid two surfaces a bonding material, which is partially polymerized toenable further rapid polymerization for bonding purposes at temperaturesnot highly elevated, and which is in a state of molecular dispersion ina quantity of a polymerizable liquid solvent material to increase theliquidity of said bonding material and permit a satisfactory bondingcontact with elemental areas of said surfaces in spite of thesubstantially large average molecular size of said partially polymerizedbonding material; and placing said two surfaces one against the otherwith the introduction therebetween of a catalyst to effect apolymerization reaction involving simultaneously said partiallypolymerized bonding material and said polymerizable solvent material ata temperature under 0. without evolution of any volatile material, atleast one of said surfaces being out from a single crystal of a polarcompound, thereby effecting strong adhesion of said last-mentionedsurface and the other of said two surfaces.

18. The process for making a transducer device having anelectromechanically sensitive element one surface of which is secured toanother similarly shaped surface comprising: applying to at least one ofsaid two surfaces a bonding material, which is partially polymerized toenable further rapid polymerization for bonding purposes at temperaturesnot highly elevated, and which is in a state of molecular dispersion ina quantity of a polymerizable liquid solvent material to increase theliquidity of said bonding material and permit a satisfactory bondingcontact with elemental areas of said surfaces in spite of thesubstantially large average molecular size of said partially polymerizedbonding material; and placing said two surfaces one against the otherwith the introduction therebetween of a catalyst to effect apolymerization reaction involving simultaneously said partiallypolymerized bonding material and said polymerizable solvent material ata temperature under 90 C. without evolution of any volatile material,both of said surfaces being surfaces of single-crystalline plates of apolar compound, thereby effecting a strong adhesion of said two platesso that piezoelectric deformations of the regions near said two surfacesin opposite senses are associated with fiexural movements of thecomposite element.

ANDREW SZEGVARI. CHARLES K. GRAVLEY.

(References on following page) References Cited in the file of thispatent UNITED STATES PATENTS Number Name Date Sawyer Dec. 22, 1936Sawyer Mar. 19, 1935 Kropa Nov. 9, 1948 Kropa Nov. 9, 1948 SingletonJune 14, 1949 OTHER REFERENCES Experimental Plastics and SyntheticResins,

16 DAlelio, Low Pressure Laminating, 1946, pp. 67-8.

Industrial and Engineering Chemistry, Polyester Styrene Resin Systems,Ebers et a1., Jan 1950, pp. 114-119.

Proceedings of the I.R.E., Standards on Piezoelectric Crystals, vol. 37,Issue 12, pp. 1378-1395, Dec. 1949.

Optical Methods of Chemical Analysis, Gibb, The Nichol Prism, pages256-7, 1942.

1. THE PRESSURE FOR MAKING A TRANSDUCER DEVICE HAVING ANELECTROMECHANICALLY SENSITIVE ELEMENT ONE SURFACE OF WHICH IS SECURED TOANOTHER SIMILARLY SHAPED SURFACE COMPRISING: APPLYING TO AT LEAST ONE OFSAID TWO SURFACES A BONDING MATERIAL, WHICH IS PARTIALLY POLYMERIZED TOENABLE FURTHER RAPID POLYMERIZATION FOR BONDING PURPOSES AT TEMPERATURESNOT HIGHLY ELEVATED, AND WHICH IS IN A STATE OF MOLECULAR DISPERSION INA QUANTITY OF A POLYMERIZABLE LIQUID SOLVENT MATERIAL TO INCREASE THELIQUIDITY OF SAID BONDING MATERIAL AND PERMIT A SATISFACTORY BONDINGCONTACT WITH ELEMENTAL AREAS OF SAID SURFACES IN SPITE OF THESUBSTANTIALLY LARGE AVERAGE MOLECULAR SIZE OF SAID PARTIALLY POLYMERIZEDBONDING MATERIAL; AND PLACING SAID TWO SURFACES ONE AGAINST THE OTHERWITH THE INTRODUCTION THEREBETWEEN OF A CATALYST TO EFFECT APOLYMERIZATION REACTION INVOLVING SIMULTANEOUSLY SAID PARTIALLYPOLYMERIZED BONDING MATERIAL AND SAID POLYMERIZABLE SOLVENT MATERIAL ATA TEMPERATURE UNDER 90*. WITHOUT EVOLUTION OF ANY VOLATILE MATERIAL,THEREBY EFFECTING STRONG ADHESION OF SAID TWO SURFACES.